The invention relates to a rotary mode change switch for a hand tool such as a rock drill or a drill driver.
When drilling a rock the sequence of switching operating modes is, for example, Drill  less than - greater than  hammer  less than - greater than  position bit  less than - greater than  cut, which can be switched, reliably and in both directions, wherein each mode is a switch step.
In hand tools having several different movement modes, one mechanical switchover is generally required for each individual operational stage. Conventionally, the switch over is done using external manual, rotationally-resistant and axially switchable displaceable switching elements such as countershafts or switch sleeves.
In rotary mode switches, the angle changeover is actuated externally on the driver part. The changeover is at least partially transformed using an eccentrically disposed pin either directly through direct rotationally-free engagement or indirectly through the translation of auxiliary switching devices into an axial movement of a switching element.
Switching of operating modes is only possible, in a form-fitting arrangement of the bilateral toothing, between the gear pairings of the transmission stages used. To achieve synchronized switching by de-coupling a reliable manually operated mode selection, the drive part can be locally fixed and the switching chain can be resiliently shifted.
DE 3618024 discloses a rotary mode change switch, which is internally spring-biased and rotatable for the synchronized switching of the operating modes of a hand tool. The switch is comprised of a manually operated driving part and an eccentrically disposed pin. The pin is arranged in a recess in the driving part and spring-biased against the recess"" eccentric inner wall by a compression spring and is formed by a plurality of locally fixed positions and is switchably moveable along the radial contour of the recess.
EP836902 discloses a mode selection switch, which is rotatable against an internal spring bias, for the synchronized switching of the operating modes of a hand tool. The switch comprises a manually operable driving member and a driven member, which is driven by an eccentrically mounted pin. The driving member and the driven member are axially fixed relative to each other. The driving member and the driven member each include an eccentrically arranged curved recess, wherein each recess is situated opposite the other recess and oriented in a rotational plane perpendicular to a rotational axis of two helical compression springs. The two springs include ends that are alternately in contact with a front face of the recess in the driver member or with a front face of the recess in the driven element. Both compression springs are constantly and axially arranged in the transitional area between the driving member and the driven member due to the relative rotation of the driver member to the driven member. The springs are identically stressed in both directions of rotation such that a mirror-symmetrical setting and biasing process results with respect to the angular shift.
The object of the present invention is to provide an alternative mode selection switch. A further object of the invention is the formation of a rotational direction dependent, non-mirror-symmetrical setting process with respect to the angular shift.
In accordance with the invention, a rotary mode change switch, which is used for the synchronized switching of the operating modes of a hand tool, comprises an external manually actuated operating driving member and a driven member. The driving member and the driven member are coaxial to each other and are mounted in a fixed and rotationally-resistant manner. Two eccentrically recesses are arranged inside the driving member perpendicular to the rotational axis. Two spring elements each include initial front surfaces that are in contact with the driving part and second front surfaces that are oriented in the same direction. At an angular shift of the driving member relative to the driven member, at least one spring element of the two spring elements is in alternate contact with an eccentrically arranged contact member of the driving member.
Consequently, due to an angular shift of the driving member relative to the driven member, only one of the spring elements arranged inside the axial area of the driving member is constantly stressed.
Preferably, the second front surface of each spring element is provided with a smooth pressure element. The smooth pressure element covers the second front surface such that a low-wear contact of the spring element at the contact member is obtained.
Preferably, the recesses in the driving member, within the rotational plane, are disposed perpendicularly to the rotational axis such that a compact construction of the rotary mode selection switch is possible.
The spring elements are, preferably, compression springs and preferably, helical in shape. As a result, in a compact construction, high bias forces with a substantially linear characteristic curve are obtained.
Preferably, the rotary mode selection switch is mirror-symmetrical. As a result, a magnitude of the bias is independent of the rotary direction relative to the magnitude of the angle shift.
The rotational position of the driving member is preferably fixed by a fixation means that is force-fittingly engaged into the indentations of the driving member. As a result, a one-time manual, externally selected operating mode opposite the housing can be set to be self-limiting. Moreover, an angle shift of the switching, associated with a switch stage corresponding to the switch sequence, up to the point of synchronized switch over of the gears, remains intact. Further, a temporarily stored bias/setting is effected within the switching chain.
The fixation means is preferably a flat spring that engages into the radial indentations of the driving member. The fixation means is technically simple to achieve.
A pin in the driven member is eccentrically arranged and preferably mounted to be freely rotational such that it can be form fitted and rotational resistant connected with a auxiliary switching device, such a as a metal bow.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.